Where or when could I find a Capture Expert charm?

See topic.

I currently have:

Full Qurupeco Armor with either Grinder jewels or Attack Jewels (depending on what I need - just random hunting in Moga Woods or actually going on a quest.)

A War Hammer +

A Rugged Great Sword (how do you think I cut Ludy's tail and wound his mane?)

The Bone Tomahawk (to be upgraded into a Qurupeco Chopper when the Pale Extract FINALLY becomes available...)

I know the Capture Expert Charm gives more rewards for captures, and I have become somewhat proficient at that.

If I have to unlock some place I haven't been to yet, so be it. Gobul stands in my way.

You probably don't have access yet to Cap Expert. It's an A level skill, so the best you can get on a talisman is +4. And I don't think they appear until High Rank.

Easiest way (only way?) offline/low rank is to get the Baggi armor set. If you're offline, Great Baggi is a 4* quest. Should be unlocked once you defeat Gobul offline. So you're close. Good luck!